I am using the MARS program to write some MIPS assembly code and the program I am writing needs to take in an input file and then iterate through it to change some numbers. I have all of the body of the code written but I am not sure how to actual take in a file. I have the following code that reads in the input and stores the address:
.data 0x0
magicNum: .asciiz "P2" #magic number
zero: .word 0
newLine: .asciiz "\n" #new line character
.text 0x3000
main:
ori $v0, $0, 8 #8 is syscall to read string
ori $a0, $0, 100 #stores address of input buffer
ori $a1, $0, 3 #max character to read in
syscall
#the rest of the code is down here
but where do I actually put the file on Windows to have it taken in?
You have to use syscall 13 to open a file, and then use syscall 14 to read from it and store its contents into a buffer.
Here's a snippet to get you started, just fill in the gaps with your code:
.data
filename: .asciiz "file.txt"
buffer: .space 1024
.text
la $a0, filename
li $a1, 0 # readonly
li $a2, 0
li $v0, 13
syscall # open file
bltz $v0, file_error
move $a0, $v0
la $a1, buffer
li $a2, 1024
read_file:
li $v0, 14
syscall
beqz $v0, read_done
bltz $v0, read_error
addu $a1, $a1, $v0 # adjust buffer pointer
subu $a2, $a2, $v0
bnez $a2, read_file # If buffer not full and not EOF, continue reading
read_done:
# File copied to buffer
# Your code goes here
file_error:
# Code to take action if file errors occur (e.g. file not found)
read_error:
# Code to take action if read errors occur
If you are using MARS the file should be located in the current directory (the place where you started MARS).